Phylum Echinoderms
- habitat and lifestyle
- examples
- free-living marine animals
- starfish, sea urchins and sand dollars
Phylum Echinoderm characteristics
- symmetry
- head
- skeleton
- water vascular system
- secondary pentamerous (five point) radial symmetry
- no cephalization, so oral surface with mouth and aboral with anus
- internal skeleton made of calcareous ossicles that may project into spines
- WVS composed of coelomic canals and tubular extensions known as tube feet or podia
Class Stelleroidea characteristics
- examples
- adult body
- central disc
Phylum Echinoderms
- sea stars and brittle stars
- adults are star-shaped
- central disc present with 5 or more radial arms
Subclass Asteroidea characteristics
- type
- body
- oral surface of each arm contains…
Star fish
- phylum Echinoderms
- class Stelleroidea
- adults are star shaped with flattened central disc and radially arranged arms which are sharply demarcated from the central disc
- ambulacral groove where numerous tube feet are located
Asterias sp.
- type
- is there anterior end
- where are arms widest
- are the spines a part of exo or Endo skeleton
- where is mouth located
- how many ambulacral grooves
(Starfish)
Phylum Echinodermata
Class Stelleroidea
Subclass Asteroidea
- no anterior or posterior
- closer to central disc
- endoskeleton
- oral surface in middle of central disc
- 5, one for each arm
Function of tube feet
Feeding, respiration (gas exchange), locomotion and excretion
Asterias sp.
- where are pedicellariae and what are their function
- where are papulae and what are their function
- between spines, remove unwanted organisms and debris from surface of the animal, and capture prey
- around spines, aboral surface. Oxygenated water flow over finger-like sacs called papulae which absorb O2 like gills
Cross section of a sea star arm
- are ossicles in epidermis or dermis
- what is the function of ossicles
- why do papulae connect to the coelom
- dermis
- provide rigidity and protection as part of endoskeleton
- papulae are site of gas exchange/ excretion
Why do you think the WVS is so important to the echinoderms
Tube feet can extend or retract based on the volume of water present in the system of the arm; allowing movement and to capture prey.
Does bipinnaria larva have radial or bilateral symmetry?
Bilateral, 2 equal halves
Why does the brachiolaria larva have adhesive arms and an adhesive sucker
Larvae sink to bottom and attach to substrate firstly with arms and then sucker
What are the advantages to the sea star of having larval stages in its life cycle
Larvae of several species can reproduce asexually before reaching maturity. When food is plentiful more reproduction. Occupy different habitats so less competition
Habitats of Bipinnaria and Brachiolaria larva
Top of water
Bottom of water
How do the arms of young sea stars compare with those of the adult
Shorter, wider with long projections off each arm
Subclass Ophiuroidea characteristics
- known as
- central disc
- ambulacral grooves
- tube feet
Phylum echinoderms
Class Stelleroidea
- Brittle stars, serpent stars and basket a stars
- central disc is sharply demarcated from the long, slender arms
- no ambulacral grooves and the small tube feet extend between plate-like ossicles on the oral surface
Brittle stars
- type
- how do arms differ from Asterias
- are ambulacral grooves present
Phylum Echinodermata
Class Stelleroidea
Subclass Ophiuroidea
- thinner, spiny, longer
- no ambulacral grooves
Gorgonocephalus sp.
- type
- unique arm feature
(Basket star)
Phylum Echinodermata
Class Stelleroidea
Subclass Ophiuroidea
-repeated branching of the arms
Class Echinoidea characteristics
- examples
- body
- ossicles
- Sea urchins and sand dollars
- adults are circular or oval in shape and do not have arms
- ossicles are flat and have been fused together to form a solid test
Echinus sp.
- type
- skeleton structure
- ambulacral area
- are spines evenly distributed
- pedicellariae?
(Sea urchin)
Phylum Echinodermata
Class Echinoidea
- flat and joined together to form solid test
- ambulacral grooves have tube feet, hard to see unless spines removed
- yes, besides around mouth
- yes
Aristotles lantern
- type
- function
Phylum Echinodermata
Class Echinoidea
-5 bulky pyramids that support 5 teeth bars and muscles. Used to scrap algae off rocks and surfaces and biting/ chewing prey. Teeth protrude from mouth.
Irregular Echinoids, such as ______ have a ______ body with secondary _______ symmetry, which may be an adaption for __________
Sand dollars
Flattened
Bilateral
Burrowing in the sand
Dendraster sp. and Mellita sp.
- type
- do they have spines
- where are tube feet openings
(Sand dollar and keyhole sand dollar)
Phylum Echinodermata
Class Echinoidea
- yes, tiny ones used for movement along ocean floor and to buy itself in the sand.
- petaloid ambulacral on aborsal side
Class Holothuroidea characteristics
- known as
- body
- symmetry
- ossicles
- tube feet
- Sea cucumbers
- elongated along oral-aboral axis and as a result shows secondary bilateral symmetry, no arms
- ossicles microscopic
- tube feet have been modified to form large tentacles at the anterior end
Cucumbers sp.
- type
- appearance
- are there arms?
- spines?
- how are tube feet arranged
- why is it in phylum Echinodermata
(Sea cucumber)
Phylum Echinodermata
Class Holothuroidea
- long, stout, oval with “arms” at Antietam end and rounded posterior end.
- no
- spikes are soft to touch and embedded in skin, so can’t see
- long rows on body arranged in 5 rows (ambulacral zone) and tentacles are modified tube feet
- calcareous spines, tube feet
